1. Field of the Invention
The present invention relates toll a living body function measurement method to observe various reactions when certain kinds of stimulations are given to a living body.
2. Description of the Related Art
The living body function measurement method is a method of observing various reactions when certain kinds of stimulations are given to the living body. Especially, the neural activity following the stimulation given to the sensory organ etc. is observed in the measurement of the brain function. That is, the following living body reactions are occurred along with the neural activity.
(1) Change in an amount of the reduced hemoglobin.
(2) Change in blood flow.
(3) Change in thickness of blood vessel.
(4) Structural changes in cell in organization.
The function in the observation portions of the brain is measured by observing these reactions.
A method of observing these reactions by using the light is well known. Especially, a technique of measuring a brain function is disclosed in T. Bonhoeffer and A. Grinvald, xe2x80x9cOptical Imaging Based on Intrinsic Signals In Brain Mapping the Methodsxe2x80x9d, Academic Press Inc. (1996), or Bonhoeffer, A. Grinvald, xe2x80x9cThe layout of Iso-orientation domains in Area 18 of cat visual cortex: Optical Imaging reveals a Pinwheel-like Organizationxe2x80x9d, J. Neurosci. 13, 4157-4180 (1993), etc. Each of these techniques is a technique of irradiating a visible light to the exposed brain, and measuring the reflected light intensity distribution on the surface of the brain as a change of stimulation.
On the other hand, the device, which measures the function of the scatterer sample of the living body etc., is disclosed in the Japanese Patent No. 2890309. In this device, the light is irradiated to the scatterer sample, and the heterodyne of the, transmitting light is detected.
However, since the living body is a scatterer, generally, when the function in the living body is measured by using the light, the reflected light from the observation point in the living body becomes very weak. Therefore, it is very difficult to perform the function measurement of the living body at deeper position than the surface to be observed.
An OCT (Optical Coherence Tomography) is known as a technique which observes the structure in the scatterer of the living body etc. (see U.S. Pat. No. 5,321,501). The example of observing the structure in the living body by using the technique of this OCT is described in SCIENCE, VOL. 254, P1178 (1991), etc. In the OCT, the structure in the sample can be observed with high depth resolution by the heterodyne detection by using the light source with low coherence. The depth resolution is almost equal to the coherence length of the light source to be used. On the other hand, in the technique disclosed in the patent above-mentioned No. 2890309, the heterodyne detection is used. However, it is difficult to obtain the high depth resolution since a use of the low coherence light is not shown. Since the technique is la method to detect the transmitting light of the sample, it is difficult to observe an especially big sample and animal sample.
An object of the present invention is to provide a technique, which performs a living body function measurement in the living body with high-resolution evaluation.
A living body function measurement method according to the present invention is characterized by comprising: separating a light from allow coherence light source into a signal light and al reference light; modulating a frequency of at least one of the signal light and the reference light; irradiating the signal light to an observation area of a living body sample; giving a stimulation to the living body sample from an outside of the living body sample; synthesizing the signal light via the observation area and the reference light and detecting a heterodyne interference signal; and measuring a living body function of the observation area by measuring a change in the heterodyne interference signal when the stimulation is changed.